Balancing redox reactions in acidic solution

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1) ClO3¯ + SO2 ---> SO42¯ + Cl¯

2) H2S + NO3¯ ---> S8 + NO

3) MnO4¯ + H2S ---> Mn2+ + S8

4) Cu + SO42¯ ---> Cu2+ + SO2

5) MnO4¯ + CH3OH ---> HCOOH + Mn2+

Answers to Probs. 1-5

6) Cr2O72¯ + Fe2+ ---> Cr3+ + Fe3+

7) HNO2 ---> NO + NO2

8) H2C2O4 + MnO4¯ ---> CO2 + Mn2+

9) O2 + As ---> HAsO2 + H2O

10) NO3¯ + I2 ---> IO3¯ + NO2

Answers to Probs. 6-10

11) HBr + SO42¯ ---> SO2 + Br2

12) H5IO6 + Cr ---> IO3¯ + Cr3+

13) Fe + HCl ---> HFeCl4 + H2

14) NO3¯ + H2O2 ---> NO + O2

15) BrO3¯ + Fe2+ ---> Br¯ + Fe3+

Answers to Probs. 11-15

16) Cr2O72¯ + C2H4O ---> CH3COOH + Cr3+

17) MnO4¯ + C2H4O ---> CH3COOH + MnO2

18) Zn + NO3¯ ---> NH4+ + Zn2+

19) NO2 + H2O --> HNO3 + NO

20) S2¯ + NO3¯ ----> NO + S8

No answers are provided for Probs. 16-20

21) CuS + NO3¯ ---> NO + Cu2+ + HSO4¯

Answer to Prob. 21


Problem #22: Ru(s) + Cl¯(aq) + NO3¯(aq) ---> RuCl63¯(aq) + NO2(g)

Solution

1) Eliminate the Cl¯ for the moment:

Ru ---> Ru3+ + 3e¯
e¯ + 2H+ + NO3¯ ---> NO2 + H2O

2) Multiply second half-reaction by 3 and add:

6H+ + 3NO3¯ + Ru ---> Ru3+ + 3NO2 + 3H2O

3) Add in the chloride:

6HCl + 3NO3¯ + Ru ---> RuCl63¯ + 3NO2 + 3H2O

4) Add in three more H+, if you wish:

6HCl + 3HNO3 + Ru ---> H3RuCl6 + 3NO2 + 3H2O

Comment: good ole aqua regia to the rescue!


Problem #23: IO3¯(aq) + I2(s) ---> I2(s) + HIO(aq)

Solution

1) Half-reactions:

10e¯ + 12H+ + 2IO3¯(aq) ---> I2(s) + 6H2O
2H2O + I2(s) ---> 2HIO(aq) + 2H+ + 2e¯

2) Multiply bottom by 5, then add:

10H2O + 5I2(s) + 12H+ + 2IO3¯(aq) ---> I2(s) + 6H2O + 10HIO(aq) + 10H+

3) Eliminate like items:

4H2O + 4I2(s) + 2H+ + 2IO3¯(aq) ---> 10HIO(aq)

4) If you wanted to recombine:

4H2O + 4I2(s) + 2HIO3(aq) ---> 10HIO(aq)

Problem #24: Someday!


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